1. Field of the Invention
The present invention generally relates to article transport systems and, more particularly, to a impact energy absorbing structures which are adaptive to mass and impact energy when an object or arbitrary size and shape is brought to a stop from a high but variable velocity.
2. Description of the Prior Art
The transport of material and objects is an important feature of many industrial activities, particularly when material or objects must be moved on a large scale. Many such systems include arrangements for sorting of objects or material in accordance with properties thereof or indicia placed on the objects. For example, large volumes of mail or packages which must be transported to different locations must first be sorted in accordance with addresses placed thereon in the course of being transported to different locations in a sorting facility. Similar systems and applications may be encountered in baggage handling in airports and the like.
Such sorting of objects requires the objects to be handled in sequence in order to provide selectivity of handling and direction to various locations from which groups of objects that can be commonly transported to another location. This requirement generally implies that the objects must be transported at relatively high speed in order to accommodate the volume of objects which are presented. While it is possible to regulate the speed of objects somewhat in a high volume sorting apparatus, it is not generally possible to provide space to allow significant deceleration of objects as they approach their final destination in the sorting machinery. Therefore, as the object approaches a final destination such as a sorting bin or a stacker apparatus (sometimes referred to as a destination pocket or, simply, pocket) in the sorting system, the acceleration must usually be quite abrupt and often involves allowing the object to impact more or less violently on a surface or barrier such as the side of a destination pocket in a largely uncontrolled motion.
Consider a simple letter envelope reaching a stacker in a mail sorting system. The speed of an envelope through a sorting system will often be in the range of one hundred to two hundred inches per second and cannot be diminished significantly as the stacker or pocket is approached. The envelope is thus generally xe2x80x9cflownxe2x80x9d into the pocket and the edge of the envelope allowed to impact a substantially rigid surface. Even though such an envelope may have a relatively low mass, the momentum may be quite substantial and will result in a rebound from the rigid surface due to the mechanical structure of the envelope, itself. That is, in regard to the above example, an envelope has two structurally dissimilar static surfaces which are joined at the edges by sharp folds; forming essentially a dual-web torsion box. One surface, however, exhibits a greater static and dynamic load-carrying capacity than the other due to the diagonal stiffeners formed by the sealing arrangement. Therefore, an impact of an edge of the envelope with a rigid surface results in an elastic columnar buckling deformation which is proportional to the mass and rigidity of the envelope. The energy of the impact with a rigid surface thus causes a state change of the principal load-bearing webs of the object and the only path for resolution of the resultant deformation-redirected energy is through an aggressive and completely unstable rebound of the object from the surface. Both the direction of the rebound and the shape and change of shape and orientation of the envelope or other object during rebound are completely unpredictable.
The rebound action and object/envelope structural instability greatly increase the likelihood of an event called a xe2x80x9ctail collisionxe2x80x9d as the rebounding product may be struck (at the originally trailing edge or other surface thereof) by the leading edge of one or more incoming objects directed to the same pocket while the space collectively occupied thereby consumes a large portion of the available space in the pocket. The result is a multiple object xe2x80x9cjamxe2x80x9d in the pocket, often with substantial attendant damage to the objects, which not only prevents intended collection (e.g. stacking) of objects in the pocket but which in also likely to increase in severity through further collisions and may propagate outward from a pocket and cause malfunctions of larger portions of the sorting system. Collisions also result in increased generation of airborne particulates and objectionably high noise levels. The cumulative effect is so frequent and severe that the mechanics of the objects and the velocity arresting process is considered to be the defining entity of the operational integrity of the entire sorting and transport system.
Attempts have been made to provide energy absorbing surfaces for arresting objects in sorting and transport systems. However, the momentum of objects in mail sorting systems and the like can vary widely as can the amount of energy which must be absorbed to limit rebound and may be further complicated by factors such as the movement of contents within an envelope or other object. Attempts to provide energy absorption to date have been found to be very limited in both amount and range of energy which can be absorbed and dissipated while presenting variable geometry in the system pockets. Therefore, while the violence of impact and rebound can be diminished somewhat by the attempts to provide energy absorbing surfaces, the motion of objects and changes in their orientation and shape have been made even more unpredictable and widely variant; resulting in virtually no improvement in prevention of collisions between objects and jamming of the transport/sorting system.
It is therefore an object of the present invention to provide an adaptive energy absorbing arrangement for arresting motion of objects in a sorting/transport system which can limit rebound of objects, provide increased uniformity of object motion in pockets and avoid collisions of objects and resulting jamming and object damage.
In order to accomplish these and other objects of the invention, a device for arresting motion of an object is provided including a lattice membrane having apertures therein, and an aperture for causing flow of fluid through the membrane when it is displaced or deformed, wherein the aperture is shaped for causing vacuum effects and vortex activity adjacent the membrane in response to the flow of fluid.
In accordance with another aspect of the invention, a method of arresting movement of an object is provided comprising steps of deflecting a apertured membrane with the object and generating vortices at apertures of the membrane in response to the deflection, wherein the vortices cause reduced pressure at a surface of the object.